Generally, a logic circuit using a magnetic tunnel junction is operated such that, when the same current flows through an input terminal, the magnetization direction of a free magnetic layer is changed, whereas when the directions of currents are different from each other, the magnetization direction of the free magnetic layer is not changed. Accordingly, the magnetic spin of the free magnetic layers within intersecting cells can be arranged in desired directions due to a combined magnetic field formed by respective currents, while the magnetization direction of a pinned magnetic layer is fixed. As a result, two types, that is, parallel and anti-parallel directions, are implemented as the magnetization directions of the two magnetic layers, so that a digital signal having logic levels ‘1’ and ‘0’ can be recorded.
Further, when a digital signal having logic levels ‘1’ and ‘0’ is read, the Tunneling Magneto-Resistance (TMR) of an MTJ device is used. When a detection voltage is applied to the MTJ device, electron carriers are tunneled through a non-magnetic and non-conductive tunneling layer between the magnetic layers, thus passing through the magnetic layers. Resistance relative to the detection current is maximized when the magnetic vectors of the pair of magnetic layers are parallel in opposite directions (anti-parallel), and is minimized when the magnetic vectors of the magnetic layers are parallel in the same direction (parallel), thus enabling resistance corresponding to the relative magnetization directions of the two magnetic layers to be measured on the basis of the conductance of electrons, which tunnel through the insulating layer.
FIG. 1 is a perspective view schematically showing a conventional Magnetic Tunnel Junction (MTJ) device. As shown in the drawing, a conventional MTJ device 100 (disclosed in IEEE Electron Device Letters, vol. 26, no. 6, p. 360, 2005) includes a top electrode 111 and a bottom electrode 113, which are provided to allow current to flow therethrough, a pinned magnetic layer 115 and a free magnetic layer 117, which are magnetic layers deposited between the top electrode 111 and the bottom electrode 113, and an insulating layer 119 deposited between the pinned magnetic layer 115 and the free magnetic layer 117 to insulate them from each other.
Further, the MTJ device includes three or more input layers 120 disposed on the top of the top electrode 111 and configured to receive current to magnetize both the pinned magnetic layer 115 and the free magnetic layer 117 of the MTJ 110, thus performing a logic operation depending on logic levels input through the input layers 120.
Further, the pinned magnetic layer 115 is pinned to prevent the magnetization direction from being changed depending on the input of respective input layers 121, 123 and 125. When the number of currents flowing in the same direction, among currents flowing through the first input layer 121, the second input layer 123 and the third input layer 125, is two or more, the magnetization direction of the free magnetic layer 117 is determined by the direction of the currents.
TABLE 1ABCR−I (0)−I (0)−I (0)RL (0)−I (0)−I (0)+I (0)RL (0)−I (0)+I (0)−I (0)RL (0)+I (0)−I (0)−I (0)RL (0)−I (0)+I (0)+I (0)RH (1)+I (0)−I (0)+I (0)RH (1)+I (0)+I (0)−I (0)RH (1)+I (0)+I (0)+I (0)RH (1)
In this case, A, B, and C respectively indicate the directions of currents flowing through the first input layer 121, the second input layer 123, and the third input layer 125, and R indicates the magnetic resistance of the MTJ device 100.
Further, referring to Table 1, when the number of identical inputs, among inputs A, B and C, is two or more, the magnetization direction of the free magnetic layer 117 is changed depending on the direction of the currents, and thus the value of the magnetic resistance is determined according to the magnetization direction.
For example, when the number of input currents corresponding to −I(0), among input currents A, B and C, is two or more, the free magnetic layer 117 is magnetized in the right direction, and the pinned magnetic layer 115 is pinned to the right direction, and thus the magnetic resistance is RL(0). When the number of currents corresponding to +I1 is two or more, the free magnetic layer 117 is magnetized in the left direction, and the pinned magnetic layer 115 is pinned to the right direction, and thus the magnetic resistance is RH (1).
In Table 1, the MTJ device 100 can drive the logic circuit given in the following Equation 1.R=A·B+B·C+C·A  [Equation 1]
However, there are problems in that, since three metal input layers are provided to change the magnetization direction of the free magnetic layer of the MTJ device, the number of processes increases and the manufacturing costs thereof increase, and in that, since current driving circuits for respective metal input layers are added, the degree of integration attributable to circuits added to the MTJ device decreases, so that it is difficult to minimize the size of logic circuits, and respective metal input layers are spaced apart from the MTJ device, with the result that current required to control a magnetization direction increases, thus increasing power consumption.